In order to achieve combustion efficiency of optimum output required to a high performance internal combustion engine that uses gasoline of high octane number, ignition is done at an angle of −5 degrees to −6 degrees (±) before top dead center (BTDC) in a case of a low revolution per minute according to respective RPMs of the internal combustion engine and advance ignition timing is also set to BTDC of 50 degrees (±) as RPM increases so as to obtain maximum output of the internal combustion engine.
A fuel supplying system includes an electronic control unit (ECU) which is mounted to an engine and supplies a predetermined amount of fuel through fuel nozzles very sensitively suitable for stoichiometric ratio in proportion to temperature change of the engine and an amount of intake air so that the function of controlling maximum fuel consumption rate of the engine can be enhanced and that exhaust of blow by gas such as hydrocarbon gas (HC), carbon monoxide (CO), carbon dioxide (CO2), etc., can be controlled resulting in optimized performance of the engine.
However, the above described mechanism for obtaining the maximum output of an engine cannot reduce emission of nitrogen oxide (NOx) and this problem is more serious in vehicles using liquefied petroleum gas (mixture of propane and butane).
In order to reduce the harmful nitrogen oxide (NOx) lower than optimal environmental regulations, an expensive emission control catalyst converter is attached to a proper portion through which exhaust gas is discharged from an engine such that the amount of the nitrogen oxide is controlled to be lower than standard environmental regulations. However, in this case, due to the fine nature of the catalyst, accumulation of the uncombusted hydrocarbon causes blocking, melting and damage of the converter.
In order to reduce discharge of the nitrogen oxide, various types of precombustion chambers such as a encapsulated type, a tube type, and a precombustion chamber to which a cover is fixed and inlet and outlet holes are proposed to promote combustion in combustion chambers and there is an attempt to improve performance and fuel combustion ratio of an engine using lean burn fuel ratio. However, since reduction of the composition of fuel ratio or overheat at the TDC brings misfire and abnormal ignition and consequently new problems such as reduction of output and lowering of performance of a high performance engine arise, the above proposal is not substantially applied to the LPG internal combustion engine.
The above-described problems, in the internal combustion engine using LPG, develope into phenomenon in which metal such as an encapsulated cover of a spark plug of a primary combustion chamber exceeds the heat range of the spark plug due to high heat in a cylinder where the high temperature combustion stroke is carried out and vortex heat source gas or detonation such as pre-ignition occurs in the compression stroke due to overheating in the next stroke caused by other reasons resulting in stopping the engine. Therefore, more reliable improvement is required.
To address this problem, this applicant proposed a spark plug including a main body, a central electrode, a pair of ground electrodes disposed close to a hollow lower end around the central electrode to form an arc shape, a flame exchanging orifice valve surrounding the pair of electrodes at the lower side of the main body to form a primary combustion chamber in which the electrodes are accommodated and to form an ignition hole in Korean Patent No. 0328490. In this patent, the spark plug includes a main ignition hole formed at the central area of the orifice valve and a cap formed with at least two auxiliary ignition holes outside of the main ignition hole and coupled with the lower side of the main body to surround the ground electrodes.
According to the proposal, some of compressed mixture fuel of an internal combustion engine is temporally ignited and burnt at an ignition timing of the engine in advance and a small scale of burning flame occurring from the ignition and burning is discharged into the main combustion chamber to ignite the main combustion chamber so that the combustion performance is maximized and that the combustion performance may be improved through the flame exchanging ignition holes through which the discharging gas passes in comparison with existing spark plugs. However, since excessively small flame is transferred to the combustion chamber, only restricted improvement of ignition performance can be obtained, and thus, a spark plug having precombustion performance by an expandable large volume in response to the purpose of an internal combustion engine and a large cylinder is required. In addition, according to the existing spark plug, the orifice valve is melted by high temperature flame so that lifetime of the spark plug is shortened or misfire may occur. Moreover, the precombustion occurs beyond heat range of the spark plug due to the orifice valve so that misfire occurs and the heat range should be adjusted properly to high performance revolutions of the internal combustion engine.